Cellulose ester photographic emulsions



CELLULOSE ESTER PHOTOGRAPHIC EMULSIONS Edwin H. Hilborn, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey N Drawing. Application August 8, 1952,

Serial No. 303,401

8 Claims. (Cl. 117-34) This invention relates to photographic emulsions in which a cellulose ester carrier is employed for the silver halide, which carrier has had incorporated therein a small proportion of ammonium carbonate or bicarbonate to render the same susceptible to penetration by water or aqueous liquids.

In the preparation of silver halide photosensitive emulsions, various carriers for the silver halide have been given consideration. In the early days of photography, the silver halide was carried by a cellulose ester, such as cellulose nitrate, but in order to preserve the susceptibility thereof to penetration by water, a wet plate procedure was used. It was recognized that once the cellulose ester had dried, the penetration thereof by processing solutions was difficult.

When it was recognized that, in the interest of convenience, dry emulsion layers were to be used, colloidal materials which exhibited susceptibility to a swelling or penetration by water were employed, and the use of cellulose esters for this purpose became of considerably less importance. Because of the ease with which processing solutions could be made to penetrate therein, gelatin became almost universally accepted as the carrier for silver halide in the making of photographic emulsions. Other colloids have been suggested for this purpose, however, such as polyvinyl alcohol, far-hydrolyzed cellulose esters and the like. Heretofore, however, the standard which governed the suitability of a material for the carrying of silver halide in photographic emulsions has been the susceptibility of that material to the action of water or processing solutions.

One object of my invention is to provide for photographic emulsion material in which a carrier is employed for the silver halide having more resistance to the eflect of water than the carriers which have been employed heretofore. Another object of my invention is to provide photographic emulsions which readily attach themselves to photographic film base, thus eliminating the necessity for the use of sublayers thereon. A still further object of my invention is to provide a photographic emulsion which facilitates the splicing of film provided therewith. A still further object of my invention is to provide photographic emulsion layers which act uniformly at various temperatures when in contact with aqueous solutions so that the processing temperatures therefor need not be as critical as those which have been employed heretofore with gelatin or other suggested carrier materials. Other objects of my invention will appear herein.

1 have found that organic acid esters of cellulose are eminently suited as carriers for silver halide in photographic emulsions when those esters are treated in accordance with my invention. I have found that by incorporating ammonium carbonate or bicarbonate or their mixture in a cellulose ester employed as the carrier for silver halide, the drying of layers of photographic emulsions made therefrom affects the physical properties of the cellulose ester and the resulting layer is readily susceptible to developing and fixing in the corresponding nited States Patent 0 "ice processing solutions. I have found that by using a cellulose ester material as the carrier for the silver halide in a photographic emulsion, various advantages are obtained over emulsions in which water-susceptible carriers have heretofore been used. One of the advantages obtained by my invention is that the emulsion layer is not susceptible to curl caused by variation in humidity conditions as is the case with photographic emulsions in which moisture has an influence thereon. Also, by the use of a cellulose ester which corresponds to or is similar to the cellulose ester employed in the film base, the necessity of subbing to cause adherence of the photographic emulsion layer to the film base is eliminated. Also, in View of the fact that both the film base and the carrier in the photographic emulsion are softened by the same solvents, the splicing of films using such emulsions is considerably facilitated. Another advantage in the use of cellulose esters as carriers in photographic emulsions is that high temperature processing solutions may be employed thereon without any danger of melting oil of the emulsion layer from the photographic film. Thus, the processing thereof may be speeded up over the time required in ordinary processing operations at normal temperatures.

I have found that when ammonium bicarbonate (ammonium acid carbonate), ammonium carbonate or their mixture is incorporated in a cellulose ester employed as the carrier for silver halide in a photographic emulsion and a coating of that emulsion is applied to a support and dried, the ammonium carbonate and bicarbonate therein is decomposed by the heat of drying and a spongy emulsion layer is obtained having a high degree of permeability to processing solutions therefor. Ordinarily the drying operation for photographic emulsion layers takes place at a temperature of at least 96 F, at which temperature ammonium carbonates decompose, forming CO2 and hills, which gases cause an opening up of the photo graphic emulsion layer.

The cellulose esters which are employed in accordance with my invention may be any of the organic acid esters of cellulose, particularly those having an acyl content corresponding, to a limited extent, to that of the cellulose ester film base to which the cellulose ester is to be applied. For instance, the ester employed as the carrier for the silver halide may be a simple ester, such as cellulose acetae, cellulose propionate or cellulose butyrate, or a mixed ester of cellulose, such as cellulose acetate propionate or cellulose acetate butyrate. The esters which have been found to be most useful for this purpose are those which contain at least 1 /2 acyl groups in every C unit of cellulose. For instance, in the case of cellulose acetate, those acetates having an acetyl value of 28- 44.8% are most useful in accordance with my invention. There is incorporated in the cellulose ester a small proportion of ammonium carbonate or bicarbonate or their mixture, which is preferably accomplished by mixing the carbonated ammonium with the organic solvent employed for the cellulose ester, either before or after the cellulose ester has been dissolved therein. The proportion of carbonated ammonium employed is not critical, as most any amount thereof, upon drying, will generate gas and cause the formation of the distended, cellular or spongy cellulose ester which has been found desirable, in accordance with my invention. As a general rule, however, it has been found to be desirable to incorporate at least an amount of carbonated ammonium in the cellulose ester equal in quantity to that ester, and in practical operations, amounts of 2 or 3 times up to 10 times the amount of the cellulose ester have been incorporated to obtain a good permeability to the eiiect of water or aqueous solutions.

After the photographic emulsion has been formed of the silver halide and the cellulose ester carrier, the latter containing ammonium carbonate or bicarbonate or their mixture, the emulsion is coated out as a thin layer upon a support, either film base or paper. in either case, it has been found that the initial application to this support of a subbing layer is usually unnecessary. After the emulsion has been applied to the support, it is then dried, such as by passing over heated rolls or by passing through a drying apparatus in which the photographic product is subjected to the drying eifect of heated air. It is desirable that the curing operation be carried out at such. a temperature that the temperature of the emulsion be more than 96 F., the temperature at which the ammonium carbonate and bicarbonate begins to break down into CO2 and NH3. After drying the photographic layer, it is then ready for use photographically, such as by exposing in a camera and developing and fixing in the conventional manner. The photographic product obtained is of a matte type, but, desired, the photographic film or paper may be treated with a very minute amount of solvent in sufficient amount to remove the matte from the silver image. Thereupon the photographic product may be dried to obtain the finished photograph. Various solvents may be employed in the preparing of emulsions as described, the solvents used depending on the cellulose ester which is to be employed and the miscibility of those solvents with water. I have found methylene chloride to be useful in this connection, but in some cases acetone, ethylene chloride-methanol, ethyl acetate or any other solvent, adapted for the purpose for which such solvent is used, may be employed. After the processing of the photographic layer, the final product may either be as is, if desired in matte form, or it may be desired to remove the matte by treatment of the emulsion layer with a solvent. By this subjecting to a solvent treatment, the matte is removed and the silver image which results is embedded in a clear support. I have found that, in the case of the emulsion layer which has been rendered porous or spongy in accordance with my invention, the silver halide is readily susceptible to treatment by various processing solutions, and, after exposure and processing, an image is obtained having good characteristics.

Photographic emulsion layers may be prepared in accordance with my invention by preparing the silver halide in a solution of the cellulose ester containing ammonium carbonate or bicarbonate, or their mixture, coating out the emulsion layer and then subjecting the layer to the elfect of heat in the drying operation. On the other hand, the composition may be prepared containing only one of the reagents which is employed in preparing the silver halide, and the composition may be coated out as a layer on film support and subjected to an elevated tem perature to form a porous or spongy surface, following which the other silver halide forming reagent may then be employed to treat the surface, thus sensitizing the same. The essential feature of my invention is that the photosensitive layer is in a porous or spongy condition whereby the silver halide is readily contacted by the processing solutions.

The following examples illustrate my invention:

Example 1 Three solutions, designated A, B and C, were prepared as follows:

A. 2% of cellulose acetate, having an acetyl content of approximately 39% and a propionyl content of 0.6%, 35% of ammonium bicarbonate and 63% of methylene chloride, were ground in a ball mill for 4 hours and then diluted with an equal volume of ethylene chloridemethanol (4:1).

B. This solution consisted of 2% of cellulose acetate of the same type as used in A, 1.25% of silver nitrate, 3% of water, 7% of methyl Cellosolve, 10% of methanol and the balance ethylene dichloride.

C. A solution was prepared consisting of 2% .of the same type of cellulose acetate as used in A and B, 1% of potassium bromide, 3% of water, 7% of methyl Cellosolve, 10% of methanol and the balance ethylene dichloride.

A photographic emulsion was obtained by mixing together equal parts of each solution, first adding C to B and then diluting with solution A all under darkened conditions. A layer of this emulsion was applied to paper, and another layer was applied to film base of the same type of cellulose ester as employed in preparing the emulsion. The emulsion layers in each case were then dried by applying hot air thereto, and they were then exposed photographically for 3 seconds, 2 seconds of which time involved the use of a No. 2 photoflood lamp. The emulsion was then developed in a developer having the following formula:

Water 16 oz.

Elon 45 grains Desiccated sodium sulfite 1 /2 oz. Hydroquinone 175 grains Monohydrated sodium carbonate 2 oz. 290 grains Potassium bromide 27 grains Water to make 32 oz.

The photographic material was then washed and fixed for 10 minutes in a fixing bath having the following formula:

Water 20 oz. Sodium thiosulfate r. 8 oz. Dessicated sodium sulfite /2 oz. Acetic acid (28%) 1 /2 fl. oz. Sodium metaborate /2 oz. Potassium alum /2 oz. Water to make 32 oz.

The photographic material was then washed and dried, whereupon a photographic image was obtained. In one case solvent was employed to remove the matte surface, and in the resulting product the silver image was embedded in a clear layer.

Example 2 There was ground together grams of ammonium bicarbonate, 10 grams of silver nitrate, 10 grams of a cellulose acetate butyrate having an acetyl content of approximately 21% and a butyryl content of approximately 26%, and cc. of ethylene dichloride. This ground up mass was then diluted with ethylene dichloride so as to impart good coating properties thereto. The composition was coated out onto the surface of a baryta-coated photographic paper. The paper was then subjected to a current of hot air to dry the same and to decompose the ammonium bicarbonate whereby a cellular or spongy layer was formed. This sheet was then immersed under darkened conditions in a 10% solution of potassium bromide and was washed and dried. The silver layer became light sensitive as a result of this treatment, and upon exposure was found to be susceptible to processing in the same manner as described in the preceding example. It was found in the case of the emulsions prepared in accordance with my invention that subbing of the film base to which the emulsion was applied was ordinarily unnecessary. Also, it was found that these emulsion layers could be processed at comparative high temperatures without any melting or other derogatory effects upon the carrier in the photographic emulsion.

In the above examples, ammonium carbonate may be used in place of all or part of the ammonium bicarbonate.

I claim:

1. A method of preparing a photographic product which comprises preparing an emulsion comprising silver halide and, as the carrier therefor, a solution of a cellulose ester of fatty acids of 2-4 carbon atoms, which ester contains at least 1 /2 acyl groups per Ce unit of cellulose having incorporated therein a carbonate of ammonium, coating the thus formed emulsion composition upon a support in the form of a thin layer and subjecting to a temperature of at least approximately 96 F. to decompose the carbonate of ammonium and impart a porous structure to the emulsion layer.

2. A method of preparing a photographic product which comprises preparing an emulsion comprising silver halide and as the carrier therefor a solution of cellulose acetate of at least 1 /2 acyl groups per Cs unit of cellulose having incorporated therein a carbonate of ammonium, coating the emulsion upon a support in the form of a thin layer and subjecting to a temperature of at least approximately 96 F. to decompose the carbonate of ammonium and impart a porous structure to the emulsion layer.

3. A method of preparing a photographic product which comprises preparing an emulsion comprising silver halide and as the carrier therefor a solution of cellulose acetate butyrate of at least 1% acyl groups per Ce cellulose unit having incorporated therein a carbonate of ammonium, coating the thus formed emulsion upon a support in the form of a thin layer and subjecting to a temperature of at least approximately 96 F. to decompose the carbonate of ammonium and to impart a porous structure to the emulsion layer.

4. A method of preparing a photographic film comprising coating onto a cellulose ester film base a photographic emulsion containing silver halide, carried by a solution of a cellulose ester of fatty acids of 2-4 carbon atoms, having at least 1 /2 acyl groups per C6 cellulose unit, and a carbonate of ammonium, subjecting the so coated film base to a temperature of at least 96 F. to decompose the carbonate of ammonium and impart a porous structure to the emulsion layer.

5. A method of preparing photographic paper which comprises coating out onto paper a thin layer of a photographic emulsion containing silver halide, a carrier therefor of a cellulose ester of fatty acids of 2-4 carbon atoms having at least 1% acyl groups per Cs cellulose unit, and a carbonate of ammonium, subjecting the thus coated paper to a temperature of 96 F. to decompose the carbonate of ammonium and impart a porous structure to the emulsion layer.

6. A method of preparing a photographic product which comprises preparing an emulsion containing silver halide, a carrier therefor of a solution of a cellulose ester of fatty acids of 2-4 carbon atoms having at least 1 /2 acyl groups per Ce cellulose unit, and ammonium bicarbonate, coating the thus formed emulsion upon a support in the form of a thin layer and subjecting to a temperature of at least 96 F. to decompose the ammonium bicarbonate and impart a porous structure to the emulsion layer.

7. A method of preparing a photographic product which comprises preparing an emulsion containing silver halide, a solution of a cellulose ester of fatty acids of 2-4 carbon atoms having at least 1 /2 acyl groups per Cs cellulose unit as the carrier for the silver halide, and normal ammonium carbonate, coating the emulsion upon a support in the form of a thin layer and subjecting to a temperature of at least 96 F. to decompose the normal ammonium carbonate and impart a porous structure to the emulsion layer.

8. A method of preparing a photographic film which comprises coating in the form of a thin layer onto a film base of a cellulose ester of fatty acids of 2-4 carbon atoms, a photographic emulsion containing silver halide, a carrier therefor of a cellulose ester chemically the same as the film base ester and a carbonate of ammonium, and subjecting to a temperature of at least 96 F. to decompose the carbonate of ammonium and imparting a porous structure to the emulsion layer.

References Cited in the file of this patent UNITED STATES PATENTS 1,952,787 Bennett Mar. 27, 1934 2,110,491 Salo Mar. 8, 1938 2,297,732 Woodward Oct. 6, 1942 FOREIGN PATENTS 836,468 France Oct. 17, 1938 496,049 Great Britain Nov. 21, 1938 OTHER REFERENCES Wall: Photographic Emulsions (1929), pages 222 to 225, Pub. American Phot. Pub. Co., Boston.

The Amateur Photographer, vol. 18, Oct. 6, 1893, page 312. 

1. A METHOD OF PREPARING A PHOTOGRAPHIC PRODUCT WHICH COMPRISES PREPARING AN EMULSION COMPRISING SILVER HALIDE AND, AS THE CARRIER THEREFOR, A SOLUTION OF A CELLULOSE ESTER OF FATTY ACIDS OF 2-4 CARBON ATOMS, WHICH ESTER CONTAINS AT LEAST 1 1/2 ACYL GROUPS PER C6 UNIT OF CELLULOSE HAVING INCORPORATED THEREIN A CARBONATE OF AMMONIUM, COATING THE THUS FORMED EMULSION COMPOSITION UPON A SUPPORT IN THE FORM OF A THIN LAYER AND SUBJECTING TO A TEMPERATURE OF AT LEAST APPROXIMATELY 96* F. TO DECOMPOSE THE CARBONATE OF AMMONIUM AND IMPART A POROUS STRUCTURE TO THE EMULSION LAYER. 